Vacuum circuit breaker



Oct. 17, 1933. v BRASCH ET AL 1,931,475

VACUUM CIRCUIT BREAKER Filed Nov. 10, 1951 T0 ACUU/VPUMP 9 VALVAQL LL V4 /l c? 1 7 Eras 0/: 4/ I 4 M Patented Oct. 17, 1933 UNITED STATES.

' 1,931,475 PATENT oF i-ci:

warms VACUUM cmoorr BREAKER Arno Brasch and Fritz Lange, Berlin, GermanyApplication November 10, 1931, Serial No. 574,214, and'in GermanyNovember 11, 1930 5 Claims.

addition to the expense, also possess certain disadvantages of apractical kind, such for example as the danger of explosion, which cannever be entirely overcome, efforts have been made to discover newprinciples of construction for the purpose of extinguishing the arcsupon the switching operation. Inter alia, vacuum switches have also beenproposed, in order to obtain short path of movement and small and cheaparrangements. These switches, however, are accompanied by thedisadvantage that the same will not operate in reliable fashion unlessthere is employed an essentially high vacuum amounting to, say, 10- mm.Hg, and since upon the switching operation there are always smallamounts of vapor formed, the vacuum continues to deteriorate as thevapor is given off. Constructions of this nature are, therefore, notcapable of use in practice. Beyond this, independent discharges are onlyto be avoided with extreme difficulty in a simple vacuum chamber in thecase of potentials of more than 200 kv. It is therefore necessary toattempt on the one hand to suppress undesirable discharges in the highpotential ranges, and on the other hand to employ a vacuum of such apoor kind that the small amounts of vapor produced upon the breakingaction have no effect on the insulating powers of the vacuum.

It is well known that every gas is composed of a large number of singlemolecules, which are continuously in motion to and fro, and thesemolecules in turn are composed of ions. These ions are also subject tomovement. It is furthermore known that the relative location of the ionswithin a gas varies in accordance with the particular pressure underwhich the gas may happen to be placed. If the gas is subjected to highpressure the ions are situated in greater proximity to each other thanin the case of a low pressure. It will be obvious, therefore, that theaverage distance which one ion requires to traverse in order to meetagainst the next varies in accordance with the pressure applied to thegas. Thus, for example, if the pressure on the gas amounts to 100 mm.Hg, this mean free path will amount-f These ions and gas cordingly, inthe following description, reference will be made in general to "chargecarriers;

For the completion of an electric circuit there are empoyed switchcontacts, which in the following description will be referred to as"electrodes, as the switching operation is performed in a chamber whichis closed off against the exterior, and in which there is a certaindegree of vacuum.

It has been found that an independent, i. e.,

undesirable discharge between two electrodes does not take place if thedistance between the electrodes is less than the mean free path of anelectron.

To be on the safe side it is desirable to make the distance between theelectrodes, say, merely one-half or one-third of the path of movement ofthe charge carriers. The electrodes must naturally be so fitted in thevessel that a path of discharge is at no point formed which is equal toor greater than the distance traversed by the carriers,-that is to say,the electrodes in the case of a particular embodiment require to betaken right up to the wall of the discharge vessel, in order to avoidany intermediate space between the electrodes and the wall, throughwhich space charge carriers, proceeding for example from the two rearsides of the electrodes over the free edge, might be capable of'movingto a greater extent than is represented by the mean free path ofmovement of the carriers with a given pressure. If the vacuum in avessel of this nature should be subject to deterioration upon theswitching operation by reason of the vapor released, the arrangement asdescribed nevertheless remains free from discharge, provided that byproper selection of the spacial disposal of the electrodes the statedratio between the electrode distance and the free path of movement ofthe charge carriers is adhered to.

Since, as already explained, the distance between the electrodesrequires to be very small, a plurality of electrodes are connected inseries in the case of relatively high potentials. This series connectionis also accompanied by the particular advantage that in the relativelyhigh potential ranges, for example exceeding 200,000 volts, undesirabledischarges are prevented. In the case of potentials above 200 ky.surface discharges occur along the inner wall of the vacuum vessel,which form the basis for an independent discharge. A surface dischargeis thus the opposite to a spark.

As to the surface discharges it is to be understood that at aninsulating surface there occurs in the case of a high and moreparticularly tangential component of the electrical field at the vacuumlimit a displacement of electricity carriers. In view of the rapidformation of the discharge it is to be assumed that electronsparticipate to a particular extent in this occurrence. This is referredto as a surface discharge (a kind of leakage discharge), although thesame differs quite appreciably from the leakage discharges which occurin connection with hightension insulators under atmospheric pressure.The difference resides principally in the fact that due to the vacuumsurrounding the insulator a dispersion of the charge carriers in theicinity of the insulator is possible to a much better degree than underatmospheric pressure. The electrodes projecting into the space initiatethe discharge, and it is, therefore, necessary to sup press thesesurface discharges if a discharge is to be prevented in a space of poorvacuum.

To avoid these surface discharges there may be employed the means setforth in the United States patent application Ser. No. 525,244, filedMarch 25, 1931, via, the inner wall of the vessel may be sub-divided insuch fashion that the same, for example, is composed of conductive orsemiconductive materials alternating with layers of insulating material.Particularly good results have been obtained by making the slidewaysbetween the single sections as long as possible. This may beaccomplished by the use of two or ,more insulating rings of differentinner diameter between the single chambers or sections. The assembly ispreferably such that alternate discs of metal and rings of insulatingmaterial, such as mica, board or the like, are placed one against theother, and the bounding faces covered with a material offering thegreatest possible pro- .tection against rupture.

the movement of the switch contacts employed,

in the breaker according toFig. 1.

Fig. 3 shows diagrammatically in conjunction with Fig. 4 the principleof the circuit breaker,

Fig. 4 being the diagrammatical view of a vacuum vessel, having depictedtherein the movement of the charge carriers of a gas.

By way of explanation as regards the assembly of the circuit breaker,reference is first made to Figs. 3 and 4. In these two figures 1 is avessel which is enclosed on all sides, and in which there prevails acertain degree of vacuum. In the vessel there are situated the twoelectrodes 2. These electrodes may be so moved in relation to each otherthat finally the same are caused to touch, thus completing a circuitconnected with the electrode leads. Suitable means are provided toensure that the maximum distance between the electrodes conforms withthe distance a, i. e., the distance between the electrodes amounts to awhen the switch is inoperative. In this the part of the wall between theelectrodes designated a would be subjected, owing to.the tangentialdisposal of the electrical field, to sufficient potentials to causesurface discharges to take place. These would then initiate a dischargebetween the electrodes. In Fig. 4 there are depicted the gas moleculesor ions which, as stated above, are in continuous motion. The arrowsindicate the exact movements performed. The pressure ,of the gas withinthe vessel 1 is so chosen that, for example, the distance between theions conforms with the distances 1) in Fig.

4. One ion or charge carrier moving in the vessel 1 is, in other words,required to traverse the distance h before it strikes against the nextone. The distance b may accordingly be referred to as the average freepath of movement of the charge carriers. When comparing Figs. 3 and 4,it will be seen that the distance a between the electrodes is smallerthan the average free path of movement I) of the charge carriers withinthe vessel. The conditions above referred to are accordingly fulfilledin a circuit breaker of this description, and the space between the twoelectrodes 2 is, for all practical purposes, free from discharge.

The construction of the circuit breaker is illustrated in Figs. 1 and 2.With regard to Fig. 1, there are provided metallic discs 4 havingburings 5 near the edge, which borings in the particular form ofembodiment shown are moved into alignment, i. e., are situated one abovethe other to form a common passage. The metallic discs 4 serve, togetherwith the insulating rings 6 and '7, to constitute the switch. The outeredges of the discs 4, the rings '1 and the discs 6 represent the wall ofthe vessel. At the centre each disc 4 is furnished with an orifice 8covered by means of a tightly fitting diaphragm 9, which in turn carrieson its outer face the actual switch contact 10. Counter-contacts 11 arefurnished on the lower faces of the discs 4. The distance a in Fig. 3is, in the case of the circuit breaker according to Fig. 1, producedbetween the contacts l0 and 11 by reason of the superimposed arrangementof the discs 4. By means of the rings 6 and 7 there are formed pocketsor chambers 12, and into these there project the inner edges of thediscs 6, so that a certain divisioning of the wall results on the linesset forth in the United States patent application Ser. No. 525,244. Theborings 5 enable the pockets or chambers 12 to be pumped out in common,so

that the same vacuum prevails in each. This vacuum is naturally sochosen that the corresponding free paths of the charge carriers aregreater than the spacing between the contacts 10 and 11.

To prevent any discharges, caused for example by reason of slidingeffect, from extending along the wall through the borings 5, the latter,as shown in Fig. 1, may be filled out with small balls or the like, suchas shot 13. The energy of any charge carriers striking against thismetallic filling is immediately compensated and destroyed, in suchfashion that a discharge is unable to take place. Regarding theoperation of the balls, it will be recognized in Fig. 1 that the space12 is bounded on both sides by the metallic surfaces of the members 4.In disregarding the disturbances which are caused by the projection ofthe contacts, the lines of force of the electrical field are accordinglydisposed for the greater part vertical to the surface from the onemember to the other. The spacing between the two members is made to besuch that in the case of the particular gas pressure prevailing in thespace 12 the average free distance of the charge carriers is greaterthan the distance between the surfaces measured in the direction of thelines of force.

At the point of the borings, which require to be provided for thepurpose of evacuation, this disposal of the field suffers disturbance.The equipotential "faces move further apart, and there is the dangerthat the charge carriers reach the speed, which is necessary forionization by collision, before they strike against the metallicconfinement of the space. It is usual in the art to ensure an evendisposal of the equipotential faces in the case of vacuum apparatus alsoat those points at which openings are necessarily provided by coveringthese openings by nets or grids. These nets, however, are relativelydiflicult to produce, and under certain circumstances possess a veryconsiderable electrostatic reciprocal. For this reason in the inventionthe nets are replaced by metal balls. These metal balls are simple toproduce and to arrange within the pumping aperture, and fulfill theirobject of compensating the potential faces to a considerably betterextent than a net. In this connection it is unimportant that the metalballs move into contact with the insulating ring 6, as a decrease in thespacing between the equipotential faces (such as also exists for examplebetween the electrodes) is always permissible. On the other handincrease in the spacing between the equipotential faces must be avoided.In lieu of the shot it is, of course, also possible to employ othermetallic bodies. For example,

. wire fabric may be inserted in one or more layers, so that, forexample, the fabric passes from one edge to the other. When using wirefabric, it is desirable to dispose the single pieces in such fashionthat the meshes are situated in staggered relation to eachother, thusincreasing the possibility of the charge carriers striking against apiece of metal.

Fig. 2 shows diagrammatically the means for actuating the circuitbreaker. All spaces 8 of the discs 4 communicate by means of pipes 14and a common feed pipe 15 with a source of pressure. This, for example,may be oil under pressure. As already mentioned above, the coverportions 9 for the spaces 8 may be constructed in the form ofdiaphragms. For this purpose the cover portions 9 may be constituted bycorrugated metal rings. Immediately oil under pressure flows through thepipes 15, 14 into the spaces 8 there is a simultaneous movement on thepart of all of the contacts 10 in the direction of the arrow P, so thatthe contacts 10 and 11 move together and the circuit is completed. Themechanical movement. of the switch contacts may'naturally also beproduced in other fashion.

The connection of the single pockets orchambers .12 may also beperformed by the provision of specially shaped passages in the discs 4,which passages, for example, may be inclined, helical or curved in orderto increase the path of sliding discharge.

The arrangement described with reference to Fig. 1 may, for example,also be fitted in a special vessel evacuated accordingly. In this casethere are provided in lieu of the borings 5 in the metallic discs 4 andinsulating rings 7 radial borings of such nature that the vacuum iscapable of even distributionover the pockets or chambers 12 between theinner face of the outer vessel and the inner boundary of the rings 4, '1and 6.

Under certain circumstances it is also possible to specially seal thesystem according to Fig. 1 situated in an outer vessel, or to pour oilinto the annular space, in order to obtain additional secure insulationagainst the exterior.

The actuating mechanism may be constructed 1 on various lines. Themetallic discs may consist of an elastic material, such as steel. At thecentre, for example, there may be provided small projections h, and theentire system, since only small differences in length are concerned, maybe pressed together. To actuate all sections simultaneously there may befurnished a throughgoing insulating rod, which is firmly connected withall of the metallic discs. In particular constructions it may be ofimportance to bore holes in the metal discs at certain distances apartso as to form an inclined passage. In this passage there may be movedthe actuating lever, and the field distribution is then such that thecharge carriers are nevertheless unable to pass freely through.

Experiments have shown that staggered disposal of the borings alone is,in the majority of cases, not sufficient to perform effectivedivisioning of the total space. such as to preclude possibility of adischarge. Possibly owing to unequal distribution of the field, or'alsoby reason of capacitative action caused by charging of the insulatedsurface, reflected or secondary and possibly also direct charge carriershave been found to pass in roundabout fashion through the singlesystems, resulting in independent discharge. It is, therefore, alwayspreferable, as stated above, to fill out the borings with metal balls,wire fabric or other suitable means.

It will be understood that no restriction is made to the specific formsof embodiment shown, and that various modifications are quite possiblewithin the meaning of the above description and the annexed claimswithout departing from the spirit of the invention.

What we claim as new and desire to secure by Letters Patent is:

l. A switch, comprising an evacuated vessel, partitions thereindefininga plurality of chambers, relatively movable contacts within eachchamber, the opposing partitions being spaced a distance less than themean free path of an electron at the pressure existing within thechambers and being of such extent and so positioned that discharges invacuum between chambers are prevented, means adapted to connect inseries the contacts in the several chambers, and means to actuate thecontacts to make and break the circuit through the switch.

2. A vacuum circuit breaker as claimed in claim 1, in which thepartitions are spaced by insulating members, the discharge path over thesurfaces of the insulating members exceeding the distance between theadjacent partitions.

3. A vacuum circuit breaker as claimed in claim 1, in which portions ofthe partitions are flexible.

4. A vacuum circuit breaker as claimed in claim 1, in which passages areprovided in the partitions for evacuating said chambers and means insaid passages permitting the removal of air and preventing thepenetration of charge carriers, said last mentioned means includinggranular conducting material.

5. A switch comprising an evacuated vessel, as in claim 1, in whichportions of the partitions are flexible anda contact is carried by eachflexiblev portion, and in which the means for actuating the contactscomprises means for admitting fluid under pressure to one side of saidflexible portions.

ARNO Basso-n. mrrz man.

